The invention relates to a collimator for an X-ray mammograph apparatus. The collimator defining a radiation field from a radiation source. The collimator includes a cone which is connected to the radiation source and which limits the radiation beam to the external dimensions of an X-ray image pickup. The collimator also includes a diaphragm which is situated in the cone and which further limits the radiation beam.
A collimator of this kind is used for so-called enlargement mammography. In this method, the diaphragm consists of an exchangeable plate which is inserted into the cone in a plane parallel to the image detector. One side of the plate is provided with a rounded recess, so that a corresponding radiation field is formed at the area of the front edge of the image pickup (the front edge is the edge of the image pickup which faces the breast of the patient during mammography). Moreover, the plate also includes at least one aperature through which a radiation field is defined near the rear edge of the image pickup in order to project patient data and the like onto the image pickup.
The size and the shape of the radiation field formed depend on the size and the shape of the recess in the diaphragm plate. In order to form another radiation field, therefore, the diaphragm plate must be replaced with a diaphragm plate having the desired recess.